In circuits conveying fluids under pressure and making use of quick couplers, it is desirable, or even required, to be guaranteed that connections are made properly. A poorly-established connection is firstly a source of leaks and secondly a risk of uncoupling which has the consequence at very least of causing the machine including said pressurized fluid circuits to break down, and if the machine is a motor vehicles, and which can constitute the cause of an accident (no pressure in pneumatic braking circuits, fuel leaking into the engine compartment leading to a fire . . . ).
Numerous manufacturers have made proposals for associating quick couplers of this type with an indicator device for indicating when a connection has been made correctly. To illustrate that known type of device, mention is made of document U.S. Pat. No. 4,946,205, and document U.S. Pat. No. 5,152,555 which describe a kind of fork with tines received in grooves of the body of the female element of the coupler, and projecting into the bore of said female element to be situated on the path of a collar of the male element. Those tines possess respective inwardly-directed catches preventing the device from being withdrawn so long as the collar of the male element is not situated level with them, where it acts as a cam to space them apart in order to release the catches. Since the position of the collar relative to the female element, when the collar is level with the tines of the fork, corresponds to coupling being properly established, the fact that the indicator device can be withdrawn guarantees the quality of the connection that has been made. One of the drawbacks of those devices stems from their very structure. The fork must be sufficiently stiff for its tines to be difficult to spread apart from each other merely by turning the fork about the axis of the coupler and using the wall of the female element of the coupler as a cam for moving the tines apart. Under such circumstances, the device presents a high degree of resistance to insertion of the male element of the coupler into the female element, and that can mislead the fitter into believing that a proper connection position has been reached. This is particularly true when the tines of the indicator device are of relatively small thickness so that inclusion of the indicator device does not add to the length of the coupler, which would make it necessary to have sliding surfaces for the collar of the male element to slide over the tines of the indicator that are slightly inclined relative to the radial plane, whereas in order to reduce the force required for penetration it would be appropriate for the sliding surfaces to be steeply inclined which would require the device to be much thicker. The compromise that is used in practice is such that the key for confirming connection can be extracted from its housing merely by being manipulated, which constitutes a drawback.
Document FR 2 705 431 discloses another solution for indicating that proper coupling has been made between the two portions of the coupler and is similar to document U.S. Pat. No. 6,082,779 which describes a variant in which the indicator is held captive.